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MEH > Lecture 18: Intro to endocrinology + appetite control > Flashcards

Lecture 18: Intro to endocrinology + appetite control Flashcards

1
Q

What is homeostasis?

A

Mechanisms that regulate and stabilise conditions of an internal environment.

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2
Q

Homeostatic mechanisms act to counteract changes in the internal environment. These mechanisms exist on all levels.

Identify some and respective examples.

A
  • Cell: [Ca2+] regulation
  • Tissue: balance between cell proliferation and apoptosis
  • Organ: kidney regulates [H2O and ion] in blood
  • Organism: thermoregulation
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3
Q

What are the components of a control system?

A

Stimulus, receptor, control centre, effector.

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4
Q

Illustrate how stimuli of a control system acts to ensure homeostasis.

A

Stimulus: detected so that the internal environment can be returned to its desired parameters.

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5
Q

Illustrate how a receptor of a control system acts to ensure homeostasis.

A

Detects stimuli and communicates with the control centre via the afferent pathway.

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6
Q

Illustrate how a control centre of a control system acts to ensure homeostasis.

A

Determines the set point after analysing the afferent input then determines the appropriate response.

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7
Q

What is the main part of the brain that contributes to the control centre?

A

Hypothalamus (which links closely to the post. + ant. pituitary gland).

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8
Q

Illustrate how an effector of a control system acts to ensure homeostasis.

A

Communicates with the control centre via the efferent pathway. Effector then causes the change: muscles, sweat glands, kidney etc.

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9
Q

Compare afferent and efferent pathway.

A

Both pathways are involved in control systems using nervous and endocrine communication.
Afferent: receptor-control centre.
Efferent: control centre-effector.

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10
Q

What is a biological rhythm?

A

A set cycle of the control centre that can vary due to any environmental changes: light. temperature, social interactions, exercise, eating/drinking patterns.

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11
Q

When passengers get off a plane after a long haul flight, they tend to be jet lagged. Suggest why this happens.

A

Due to a mismatch between the environmental cues and body clock (set biological rhythm).

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12
Q

Circadian rhythms are set cycles of the control centre which can be affected by environmental cues.

Which elements are under the influence of a circadian rhythm?

A

Body temperature
Cortisol
Melatonin
Appetite control

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13
Q

Compare and contrast negative and positive feedback, providing 2 examples for each.

A

-ve: a response which reverses the direction of change eg: BP control, blood glucose hormones, thermoregulation.

+ve: response that reinforces the change of direction even more eg: ovulation hormones, blood clotting, uterine contraction (oxytocin).

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14
Q

Body water homeostasis is an example of a feedback system.

In light of this, describe the body water distribution in a 70 kg adult male.

A

~ 42L total water

~ 28L ICF (2/3)
~ 14L ECF (1/3)

From ECF:
~ 11L ISF (3/4)
~ 3L Blood plasma (1/4)

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15
Q

How many L of blood would a 70kg adult male have?

A

5L

3L=blood plasma
2L= red blood cells

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16
Q

Distinguish between osmolarity and osmolality.

A
  • Osmolarity is the number of osmoles per litre of solution (VOLUME)
  • Osmolality is the number of osmoles per kilogram of solution (MASS)
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17
Q

What monitors the osmotic pressure of blood plasma?

A

Hypothalamus osmoreceptors

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18
Q

Serum osmolality is useful when investigating hyponatraemia.

What is the normal range of this?

A

275 - 295 mOsmol/kg

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19
Q

Where and what does ADH do?

A

Hypothalamic ADH is a hormone (secreted by the post. pituitary during thirst), increasing reabsorption of H2O from the kidney collecting ducts.

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20
Q

Describe the ADH control system that regulates osmolality in body fluid homeostasis.

A
  1. High blood osmolality (dehydration) detected by hypothalamus osmoreceptors.
  2. Causes more post. pituitary ADH secretion.
  3. More H2O reabsorbed from kidney collecting duct.
  4. Hence only small amount of conc. urine released.
  5. Blood osmolality is lowered to desired parameter.
  6. ADH secretion inhibited.

Negative feedback: vice versa if there is a low blood osmolality as well.

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21
Q

Illustrate the control system set by the homeostatic regulation of blood glucose levels in terms of insulin and glucagon.

A
  1. Fed state: blood glucose levels increase > 5mM
  2. Pancreas β cells secrete more insulin.
  3. Stimulates liver glycogenesis and glucose uptake into muscles + adipose via GLUT4.
  4. Blood glucose decreases to 3-5mM.
  5. Pancreas decreases insulin secretion.
  6. Fasted state: blood glucose levels decrease<3mM
  7. Pancreas α cells secrete more glucagon.
  8. Stimulates liver glycogenolysis.
  9. Glucose released into blood and increases to 3-5mM.
  10. Pancreas decreases glucagon secretion.
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22
Q

What is the endocrine system?

A

A collection of glands located throughout the body.

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23
Q

What are hormones and what do they do?

A

Chemical signals produced by endocrine glands/tissues that travel in the bloodstream to cause an effect on other tissues.

24
Q

Identify 3 major endocrine glands

A 
Hypothalamus 
Anterior pituitary gland
Pancreas
Thyroid
Parathyroid
Ovary
Testis
Pineal gland
Thymus
Adrenal gland
25
Q

There are organs and tissues that can release important hormones.

Identify 3 minor endocrine glands.

A 
Liver
Heart
Kidneys
Stomach
Adipose
Placenta
26
Q

There are 4 different mechanisms of communication via hormones.

Name and describe them.

A

Paracrine: hormone signal acts on adjacent cell via interstitial fluid.

Autocrine: hormone acts on the original cell.

Endocrine: hormone acts on target cells/tissue via the bloodstream.

Neurocrine: neuronal hormone is transported down axon into the bloodstream to reach target tissue.

27
Q

Describe 3 similarities between the endocrine and nervous system.

A
  • Both neurons and endocrine cells can be depolarised.
  • Both have secretion ability (neurotransmitters & hormones)
  • Some signalling molecules (dopamine) act as neurotransmitter & hormones
  • Both systems work in parallel to control homeostasis
  • Both mechanisms involve interactions with specific receptors on target cells to produce a response.
28
Q

Describe 4 differences between the endocrine and nervous system.

A
  • E uses hormones as signalling molecules whereas N uses neurotransmitters & action potentials
  • Nature of E. system is purely chemical but N can be both chemical and electrical.
  • Hormones travel in the bloodstream whereas neurotransmitters & action potentials travel across synapses & along axons respectively.
  • E responses are much slower than N responses after interacting with the target cell receptor.
29
Q

What are the 2 ways of classifying hormones?

A

Whether they are water/lipid soluble

What the hormones are made of.

30
Q

Name the 4 classes of hormones and give some examples.

A

Steroid: aldosterone, testosterone, cortisol

Peptide/polypeptide: insulin, glucagon, GH

Amino acid derived: adrenaline, noradrenaline, T3,4, melatonin

Glycoproteins: LH, FSH, TSH

31
Q

Give some features of steroid hormones.

A
  • All derived from cholesterol
  • All lipid soluble
  • Steroidogenic tissues convert cholesterol to different hormones
32
Q

Give some features of peptide/polypeptide hormones.

A
  • Largest group of hormones
  • Made of short chains of AA
  • All water soluble
33
Q

Give some features of glycoprotein hormones.

A
  • Protein macromolecules
  • Made of subunits
  • Has a carb. side chain
  • All water soluble
34
Q

Give some features of AA derived (amine) hormones.

A
  • Made from aromatic AA
  • Adrenal medulla (catecholamines) hormones = water soluble
  • Thyroid hormones = lipid soluble
35
Q

How are hormones transported?

A

Other than peptide hormones & adrenaline, most hormones must bind to specific proteins.

36
Q

What happens to the hormones when they are bound to their specific carrier protein?

A

They become biologically inactive where only the free form is active.

37
Q

In terms of hormone transport, describe the 3 roles of carrier proteins…

A
  • increase the solubility of hormone in plasma
  • increases half life of hormones
  • readily accessible reserve of hormones
38
Q

There are 3 factors that determine the hormone levels in the blood. Name them.

A
  1. The rate of production, including regulating syn. and secretion.
  2. Rate of delivery eg: higher blood flow to target cells/tissues/organs means more hormones delivered.
  3. Rate of degradation: how quickly hormones are metabolized then excreted.
39
Q

How would you describe the level of hormones circulating in the blood?

A

Very low concentration.

40
Q

How do hormones exert their effects on cells/tissues/organs?

A
  1. Hormones secreted from endocrine tissues to bloodstream.
  2. Hormones travel to the target C/T/O where they will only interact with specific C/T/O.
  3. The hormones do this by binding to complementary receptors that the target cells express.
  4. Cells with no/non-complementary receptors won’t respond to the hormone.
41
Q

What’s the difference between how water/lipid soluble hormones exert their effects?

A

Water soluble bind to cell surface receptors whereas lipid soluble bind to intracellular receptors.

42
Q

Which type of hormone (water/lipid soluble) would be quicker at producing an effect and why?

A

Water soluble would be quicker than lipid because water soluble receptors are on the cell surface whereas the latter are intracellular: hormones would need to enter the cell first in order to bind to the receptor.

43
Q

What causes obesity in terms of energy?

A

Chronic imbalance where energy intake > energy expenditure resulting in BMI < 30kg/m2

44
Q

Where is the appetite control centre located and specifically which part plays the central role?

A

Hypothalamus: specifically the arcuate nucleus (clusters of neurones).

45
Q

Neuronal, nutrient & hormonal signals are processed by primary neurones in the arcuate nucleus.

Identify the 2 types of primary neurones and briefly explain what they do.

A

Stimulatory neurone: contain NPY & AgRP which promotes hunger.

Inhibitory neurone: contains POMC (secretes neurotransmitters α-MSH & β-Endorphin) that promotes satiety.

46
Q

How do 1° neurons transmit signals for appetite control?

A

1° neurons synapses with 2° neurones in the hypothalamus which alters feeding behaviour.

47
Q

Hormone signals from the gut are also involved in appetite control.

Name those 2 hormones.

A

Ghrelin

PYY

48
Q

How does ghrelin stimulate hunger?

A

Stomach wall releases ghrelin when empty.
This stimulates excitatory 1° neurones in the arcuate nucleus which stim. appetite.
Inhibited when stomach filled.

49
Q

How does PYY suppress hunger?

A

Ileum/colon releases PYY when fed.

Inhibits arcuate nucleus excitatory neurones and stim. inhibitory neurones so suppresses appetite.

50
Q

What is leptin and insulin, what’s their role in appetite control?

A

Peptide hormones released by adipocytes into blood. It stimulates inhibitory & inhibits excitatory neurones. Thus, suppresses hunger.
Leptin is more significant compared to insulin in this aspect.

51
Q

Aside from appetite control, what other function does peptide hormone leptin have?

A

Induces uncoupling protein expression in the mito. Therefore, no ATP syn. occurs & energy is lost as heat.

52
Q

Which hormones signal from the body to the hypothalamus regarding appetite control?

A

Leptin
Insulin
Amylin

53
Q

Describe amylin and its role in appetite control.

A

Pancreatic β cells secrete this peptide hormone.

Suppresses appetite, decreases glucagon secretion, slows gastric emptying.

54
Q

Clinically what can pramlintide (amylin analogue) be used for?

A

Management for type 2 diabetes as it suppresses appetite.

55
Q

Which pathway is orexigenic and anorexigenic?

A 
Orexigenic = Stimulate appetite by stimulatory 1° neurones & neurotrans: AgRP+NPY.
Anorexigenic = inhibits appetite by inhibitory neurones & neurotrans: αMSH from POMC.

MEH (10 decks)

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